The invention relates to a sterility indicator device comprising a steam permeable base, indicator ink spots mounted thereon, an impermeable transparent cover film bonded to a substantial portion of the top surface of the base overlaying the indicator ink spots and to the bottom surface of the base.
More particularly, the present invention relates to an improved sterility indicator device which relies on time, temperature and steam to cause a color change in an indicator ink spot.
It is well known in the prior art that heat in conjunction with moisture will destroy micro organisms, a thorough discussion of which is presented in U.S. Pat. No. 3,981,683, Larsson et al, entitled TEMPERATURE RESPONSIVE STERILITY INDICATOR.
There have been numerous attempts by the prior art to develop chemical sterilization indicators, see for example U.S. Pat. Nos. 3,360,337, 3,652,249, and 3,341,238.
As pointed out in the Larsson Patent's discussion of the prior art, not only is the time/temperature relationship important in killing micro organisms but this relationship must also be dependent on the presence of moisture for complete sterilization. In the absence of moisture spore kill at 250.degree.-270.degree. F. is negligible, but in the presence of steam at these temperatures spore kill essentially complete in 2-12 minutes.
Thus for a chemical based sterility indicator to effectively indicate conditions of spore kill its function must be dependent upon time--temperature--and moisture, e.g. saturated steam.
Chemical indicator inks such as for example chromium chloride have been used in autoclaves for verifying the sterility conditions of rubber goods, instruments, basins, other nonporous materials, hospital lab clothing, bed linens, sponges and other items which may become contaminated by bacteria. The indicator inks may be formulated so as to be sensitive to particular time--temperature--and saturated steam conditions for given sterilization requirements.
A number of inks upon reacting with saturated steam during the sterilization process release corrosive reaction products which attack and damage extensively the items being sterilized. For example indicator inks formulas containing anhydrous chromium chloride (C.sub.r Cl.sub.3) function as excellent indicators of time/temperature/saturated steam conditions within the autoclave, however upon reacting with saturated steam produce highly corrosive hydrochloric acid and/or chlorine gas. Substantial damage results when either the gas, the acid or both come into contact with any of the sterilized goods, particularly hospital or laboratory clothing, bed linens, and similar items constructed of naturally occurring or synthetic fibers.
Old solutions to this problem have been to contain the indicator devices in small transparent plastic holders. These holders, however, created an additional expense, were easily misplaced, cumbersome to use and did not provide the stringent quality control necessary in sterilization procedures.
The instant invention overcomes the defects of the prior art by the lamination of a clear impermeable protective covering over the indicator ink spots and the base on which the ink spots are mounted so as to contain any corrosive reaction products within the indicator preventing their contact with the sterilized goods while providing a prepackaged, easy to use reliable device for ascertaining whether sterilization conditions have been met.
It is, therefore, an object of this invention to provide a chemical sterilization indicator device which contains a steam permeable, absorbent base, indicator ink or inks mounted thereon, an impermeable transparent covering film for preventing the escape of corrosive reaction products bonded to a substantial portion of the base, and an adhesive substance for bonding the covering to the base.
It is a further object of this invention to provide a protective covering and means to adhere the covering to the base which, when exposed to autoclave sterilization, will be capable of retaining their clarity and not interfere with the visual display of the indicator device, e.g. observing the color changes of the indicator inks.
It is another object of this invention to provide a chemical sterilization indicator that will not react to dry heat but will react only when steam has been present during the sterilization process. Thus by this failure to react will warn of the presence of air in the sterilizer.
Another object of the present invention is to provide a chemical sterilization indicator which when exposed in an autoclave, will indicate whether conditions of under sterilization, correct sterilization or over sterilization have occurred.
It is still a further object of this invention to provide a chemical sterilization indicator which provides a permanent record of the time/temperature/saturated steam conditions within sterilization equipment .